Idiomatic expressions are problematic for most sentiment analysis approaches, which rely on words as the basic linguistic unit. Compositional solutions for phrase sentiment are not able to handle idioms correctly because their sentiment is not derived from the sentiment of the individual words. Previous work has explored the importance of idioms for sentiment analysis, but has not addressed the breadth of idiomatic expressions in English. In this paper we present an approach for collecting sentiment annotation of idiomatic multiword expressions using crowdsourcing. We collect 10 annotations for each idiom and the aggregated label is shown to have good agreement with expert annotations. We describe the resulting publicly available lexicon and how it captures sentiment strength and ambiguity. The Sentiment Lexicon of IDiomatic Expressions (SLIDE) is much larger than previous idiom lexicons. The lexicon includes 5,000 frequently occurring idioms, as estimated from a large English corpus. The idioms were selected from Wiktionary, and over 40% of them were labeled as sentiment-bearing.